Spark plug



Oct. 25.1927.

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SPARK PLUG Filedflune 25. 1921- A. E. M DONALD Alla/my;

Patented Oct. 2 5, 1927. V

NIT STATES.

Laurea- PATENT o'FF'IcE.

v ARTHUR nnunsriviacnounrin; ortounotu; ENGLAND.

SPARK PLUG;

Application filed June 25, 1927, $eria1No; 201,371, and in Great Britain September 30, 1925.

This invention relates to spark plugswfor internal combustion engines, and more particularly to plugs of the typelinwhichan insulator supporting the central electrode is fitted to the body of the plug by means of a part-spherical or like seating adapted to form a gas-tight joint without the use of packing or cement at such seating.

The invention has for its main object to 1 provide an improved seating for the central electrode at the surface where it bears upon the said insulator.

The invention has also for its object to permit slight distortion of the component parts of the plug when subjected to heat,

without such distortion affecting the gastightness of the two seatings.

A further object of the invention is to allow for slight inaccuracies in the manuobliquity of its axis relative to the surface at which the central electrode bears upon said insulator.

The invention is hereafterdescribed with reference to the annexed drawings, in which facture of the main insulator, such as surfaces 7' ffllwhichconstitute a balljoint connection between the. two .parts .of the electrode, and thence through the main in sulator a; to the seating of the latter upon the detachable ring nut.

It will be observed that, even if the seating for the cup-washer f is slightly out of truth with the axis of the insulator, proper gas-tight joints are obtained both between the collar f and the cup-washer f and between the cup-washer f and the insulator end a by reason of the universal selfaligning effect of the ball joint f 7.

In the form of construction represented in Figure 3, the main insulator a is arranged in an inverted position as compared with that described above, its shoulder a seating upon a corresponding annular surfacec 0nthebottom of a ventilated chamber j in the plug body. The electrode stem is formed in two parts f, is, connected by a ball joint, and is partly exposed for cooling inside the chamber j. The stem 7r,- passes down through the upper insulator c and has its lower end 70 engaged with a collar or head i termiw nating the electrode. stem f and bearing Figure l is a sectional elevation of one against the top end a of the main insulator;

form of construction, and Figure 2 is a detail of the electrode. Figure 8 is a simian lar view of another form of construction.

The form of construction represented in Figures 1 and 2, employs a main insulator a enclosed in a recess 1) in the plug body 0 and carried by a ring nut d detachably connected to the body 0, and an outer insulator e seated in the ring d around the projecting stem f of the central electrode, with the usual terminal nuts 9 and a tensioning spring 72, arranged upon its upper end. The main insulator a has an annular shoulder a of convex bevelled or conical shape at about the. middle of its exterior surface, this shoulder fitting in a gas-tight manner against a corresponding concave seating on the inside of the detachable ring nut d. The central electrode is provided with a ball member or collar 7, preferably integral therewith, and having an annular face f of part-spherical shape which bears upon a similar surface f on a small cup-washer f of nickel or other suitable material, forming part of the electrode and bearing against the lower end a of the main insulator a. The tension produced in the central electrode stem j by the spring h at its upper end is transmitted by the collar 7 through the this head is cupped at f" to receive'the tip of the upper electrode stem 76, which is pressed down by an elastic disc m enclosed in a cap m secured to the top of the upper insulator e, the tip 10 of the electrode stem 70 thus centering itself automatically in the cup 7 upon the electrode stem f. The upper in-- sulatore in turn is held in the plug body by anotched or apertured ringa screwed into the top of the chamber j, a bevelled shoulder 6 upon this insulator being pressed against the ring a by the reaction of the elastic discv m the lower end of the upper insulator 6 extends down to the level of the electrode head or collar 7, so as to to this part of the electrode.

In the two constructions illustrated, a self-adjusting or universal motion is allowed by the collar f (Figure 1) or the tip k of the electrode stem 76 (Figure 3) and the cup f (Figure 1) or f (Figure 3) of the electrode, which form in effect a self-centering ball-joint so that the gas-tightness of the insulator is not affected by slight inaccuracies in the manufacture.

The insulators employed may be of any suitable material; the main insulator is preferably of fused silica, which allows the formation of gas-tight joints by grinding the allow access of air faces into their seatings in the well known manner.

WVhat I claim is A spark plug comprising a body portion having upper and lower seatings therein, an

upper insulator in engagement with the upper seating, a lower insulator in engagement with the lower seating, a cupped washer locatd at the end of the lower insulator remote from its seating and having a concave part-spherical surface, an electrode extending through the two insulatorsand cupped a self-aligning ball joint therewith, and

means for exerting pressure through said electrode and ball joint connection to hold the said insulators upon their respective seats 20 to form gas-tight joints. In testimony whereof I hereunto afiix my signature.

. ARTHUR NEST 'MAGnoNALD. 

